1: Q or (R and S) 2: (Q -> T) and (T -> S) | S 3: Assume Q 4: Q -> T 2 Conjunction Elimination 5: T 3,4 Modus Ponens 6: T -> S 2 Conjunction Elimination 7: S 5,6 Modus Ponens 8: Assume ~Q 9: R and S 1,8 Disjunctive Syllogism 10: S 9 Conjunction Elimination 11: :. S 3-7,8-10 Law of Excluded Middle